Several top House Democrats have warned President Donald Trump not to influence or discourage his former personal lawyer Michael Cohen‘s upcoming testimony before Congress, as this could be considered a crime.

Rep. Elijah Cummings (D-MD), the chairman of the House Oversight Committee, was among the many lawmakers who cautioned Trump against blasting Cohen, who is set to testify before the committee on Feb. 7 about work he performed for the president as his “fixer.”

“Our nation’s laws prohibit efforts to discourage, intimidate or otherwise pressure a witness not to provide testimony to Congress,” the chairmen wrote in a statement. “The president should make no statement or take any action to obstruct Congress’s independent oversight and investigative efforts, including by seeking to discourage any witness from testifying in response to a duly authorized request from Congress.”

Trump has repeatedly slammed Cohen on Twitter as “weak” and accused him of lying about his work for the president as a way to obtain a more lenient deal from prosecutors, a sentiment he reiterated in an interview with Fox News on Saturday night. Last month, Cohen was sentenced to three years in prison for multiple charges including bank and tax fraud, and for his involvement in making hush money payments to Trump’s alleged former mistresses. Cohen directly implicated Trump in these payments, a revelation that has raised questions about a potential indictment and impeachment.

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Cohen also confessed in November to lying to Congress about his involvement in a Trump Tower real estate deal in Moscow in 2016.

“He’s in trouble on some loans and fraud and taxicabs and stuff that I know nothing about,” Trump said in Sunday’s interview with Fox News host Jeanine Pirro. “And in order to get his sentence reduced, he says, I have an idea, I’ll tell — I’ll give you some information on the president.”

On Sunday, The New York Times reported that Cohen’s father-in-law Fima Shusterman — whom emigrated from Ukraine in 1975 — once pleaded guilty to “evading federal reporting requirements for large cash transactions. After striking a plea deal with prosecutors, Shusterman was sentenced to probation.

Several lawmakers have said Cohen’s impending testimony could prove as historic as that of John Dean, Richard Nixon’s White House counsel who testified in 1973 before the Senate committee that was investigating the Watergate scandal.